Examine the list of e-mail messages in Figure 5-55. Using the structure and example data items in this list, do the following:
A. Create a single-entity data model for this list. Specify the identifier and all entities.
B. Modify your answer to A to include entities SENDER and SUBJECT. Specify the identifiers and attributes of entities and the type and cardinalities of the relationships. Explain which cardinalities can be inferred from Figure 5-55 and which need to be checked out with users.
C. The e-mail address in the From column in Figure 5-55 is in two different styles. One style has the true e-mail address; the second style (e.g., Tom Cooper) is the name of an entry in the user's e-mail directory. Create two categories of SENDER based on these two styles. Specify identifiers and attributes.
